The present invention relates to a display panel and a manufacturing method for the display panel. The invention in particular relates to a panel construction that efficiently reduces noise.
PDPs (plasma display panels), which are one type of gas discharge panel, are currently receiving high expectations as large displays that can realize screen sizes of forty inches or more. PDPs are self-luminous type and have excellent properties such as fast responsiveness and wide viewing angles. In addition, PDPs can be manufactured relatively easily. For these reasons, PDPs are known to be suitable for large displays.
FIG. 1 shows an AC (alternating current) PDP. This PDP has a front panel member 100 and a back panel member 200 which are put facing each other. The front panel member 100 and the back panel member 200 are sealed together by a sealing material (not illustrated) which is interposed at the outer edges of their facing surfaces.
The sealing is done in the following way. First, the two facing panel members, which are held by a clip or the like at their outer edges, are heated to soften the sealing material. After this, the construction is cooled to cure the sealing material.
When the sealing is done in this way, however, the center of the construction may bulge above and below to some extent, as shown in FIG. 2. This being so, during actual drive time (when the PDP is actually driven), small vibrations occur in areas where the two sealed panel members are in contact with each other, especially in areas 203 where barrier ribs 202, which are provided in the back panel member 200 to form channels for phosphor layers 201, are in contact with the front panel member 100. Such vibrations may incur collision sounds, thereby causing noise. If the noise level of such noise increases, user discomfort intensifies. For example, a large display such as a PDP may be placed in a relatively quiet location such as a hospital as a guide display. In this case, noise is likely to be very noticeable. For this reason, panels that generate noise will end up being defective products.
On display panels such as PDPs that are driven according to a frame timesharing image display method, one frame of image is displayed by repeating four operations of set-up, write, illumination sustain, and erase. Note here that the aforementioned actual drive time refers to the time during which the panel undergoes the repetition of these operations.
Also, a panel that does not generate noise under normal conditions may generate noise when used at high altitudes of several thousand meters. This can be explained as follows. The panel inherently has small bulges, but is kept from bulging because the front and back panel members are pressed from outside due to the difference between the gas filling pressure inside the panel and the atmospheric pressure. However, when used at high altitudes, the difference between the internal pressure and the atmospheric pressure decreases, and so the forces that press the front and back panel members from outside weaken. This causes the panel to bulge.
The present invention was conceived in view of the problem described above, and has an object of providing a display panel such as a PDP that can reduce noise caused by collision sounds which occur when a front panel member and a back panel member vibrate during actual drive.
The stated object can be achieved by a display panel including a first panel member and a second panel member which are set facing each other, wherein the first panel member has a first electrode, the second panel member has a second electrode, and an image is displayed according to a frame timesharing image display method by applying voltages to the first electrode and the second electrode, characterized in that a noise level of noise in a frequency range of 20 Hz to 20 kHz, which occurs in a display area when the first panel member and the second panel member vibrate while the display panel is being driven, is no greater than 30 dB.
The present invention focuses on a band of frequencies 20 Hz to 20 kHz which correspond to the sounds human ears can detect (audible sounds), and limits a noise level to 30 dB or below in this frequency range. The noise level referred to here is ten times the common logarithm of the ratio of A-weighted squared sound pressure to the squared reference sound pressure of 20 xcexcPa. That is, the noise level is the A-weighted sound pressure level (see JIS (Japanese Industrial Standards) Z8731). In other words, the present invention reduces a noise level focusing only on a band of frequencies of sounds which are audible to humans as noise, since sounds of other frequencies not audible to humans do not pose any problem in this case. Noise is especially likely to occur during a set-up operation which is frequently repeated within one frame using relatively large voltages. Therefore, it is of particular importance to reduce a noise level in display panels that employ the frame timesharing image display method.
As a measuring instrument, a device that complies with JIS C1505-1988 or IEC (International Electrotechnical Commission) 60651 or 60804 is used. One example of such a device is precision integrating sound level meter NL-14 with 1/1 or 1/3 octave filter model NX-05 (produced by RION Co., Ltd). Measurements are performed with a microphone positioned at a vertical distance of 50 mm from the glass substrate on the panel display surface (with an entry angle of 0xc2x0).
First, the noise level of background noise is measured in the state where the panel is not emitting light. Here, it is preferable to perform measurements at several locations on the panel display surface. These measurements are carried out while varying the center frequency of a filter from 20 Hz to 20 kHz. Next, the noise level is measured at the same locations in the state where a monochromatic (e.g. white color) fixed display is being performed on the entire panel display surface, in the same way as above. The value obtained by subtracting the noise level measured during non-illumination from the noise level measured during illumination is the noise level of noise which occurs during actual drive.
The stated object can also be achieved by a display panel including a first panel member and a second panel member which has a plurality of strip-shaped barrier ribs, the first panel member and the second panel member being sealed together by a sealing material that is provided between the first panel member and the second panel member in a peripheral area which surrounds the plurality of barrier ribs, characterized in that the first panel member and the second panel member are connected to each other by a connecting material that is provided on top of at least one of the plurality of barrier ribs.
With this construction, the noise level of noise in the frequency range of 20 Hzxe2x80x9420 kHz, which occurs in the image display area when the first panel member and the second panel member vibrate during actual drive, can be limited to 30 dB or below.
Here, if the connecting material is provided on the entire top surface of each barrier rib, there will be no gaps between the first panel member and the second panel member. Hence the occurrence of crosstalk can be prevented.
Also, even when the panel is used at high altitudes of several thousand meters, the center of the panel is kept from bulging. This keeps noise and crosstalk from increasing.
The stated object can also be achieved by a display panel including a first panel member and a second panel member which has a plurality of strip-shaped barrier ribs, the first panel member and the second panel member being sealed together by a sealing material that is provided between the first panel member and the second panel member in a peripheral area which surrounds the plurality of barrier ribs, characterized in that the first panel member and the second panel member are connected to each other by a connecting material that is provided in a non-display area.
The stated object can also be achieved by a display panel including a first panel member and a second panel member which has a plurality of strip-shaped barrier ribs, the first panel member and the second panel member being sealed together by a sealing material that is provided between the first panel member and the second panel member in a peripheral area which surrounds the plurality of barrier ribs, characterized in that a projection is formed on a surface of the first panel member facing the second panel member, and the first panel member and the second panel member are connected to each other by a connecting material in areas where the projection intersects the plurality of barrier ribs.
With these constructions, the noise level of noise in the frequency range of 20 Hzxe2x80x9420 kHz, which occurs in the image display area when the first panel member and the second panel member vibrate during actual drive, can be limited to 30 dB or below.
Also, even when the panel is used at high altitudes of several thousand meters, the center of the panel is kept from bulging. This prevents noise and crosstalk from increasing.
Here, the display panel may further include a plurality of light emission cells that are aligned with intervals, wherein the projection is formed between adjacent light emission cells.
With this construction, the connecting material is kept from entering into the cells, with it being possible to prevent a decrease in cell opening ratio.
Here, the projection may have a shape of a continuous strip that extends from one side of a display area to an opposite side of the display area so as to be orthogonal to the plurality of barrier ribs, the display area being defined by the alignment of the plurality of light emission cells.
Here, the projection may have a shape of a plurality of dots.
Here, the projection between adjacent light emission cells may be formed using a dark-color material.
Here, the first panel member may have a dielectric layer, wherein the projection is formed on the dielectric layer using a same material as the dielectric layer.
The stated object can also be achieved by a manufacturing method for a display panel including a first panel member and a second panel member which has a plurality of strip-shaped barrier ribs, the first panel member and the second panel member being sealed together by a sealing material that is provided between the first panel member and the second panel member in a peripheral area which surrounds the plurality of barrier ribs, characterized by including the steps of: providing, before the first panel member and the second panel member are sealed together, the sealing material in a peripheral area of the first panel member or the second panel member so as to form a height that is greater than a height of the plurality of barrier ribs; and sealing, after the sealing material providing step, the first panel member and the second panel member by softening the sealing material while pressing the first panel member and the second panel member against each other in an area which is more central than the peripheral area.
With this method, the sealing is performed so that there will be no gaps between the barrier ribs and the first panel member. Accordingly, the noise level of noise in the frequency range of 20 Hzxe2x80x9420 kHz, which occurs in the image display area when the first panel member and the second panel member vibrate during actual drive, can be limited to 30 dB or below.
Here, in the sealing step, the first panel member and the second panel member may be pressed against each other in a center area.
Here, in the sealing step, the pressing may be performed using a difference between a pressure inside the display panel and a pressure outside the display panel.
Here, in the sealing step, the pressing may be performed using a magnetic force between magnets of opposite polarity which are positioned so that the first panel member and the second panel member lie therebetween.
Here, in the sealing material providing step, the sealing material may be provided so as to form a height that is no smaller than a sum of the height of the plurality of barrier ribs and an amount of deflection, waviness, and warping of the first panel member and the second panel member.
The stated object can also be achieved by a display panel including a first panel member and a second panel member which has a plurality of strip-shaped barrier ribs, the first panel member and the second panel member being sealed together by a sealing material that is provided between the first panel member and the second panel member in a peripheral area which surrounds the plurality of barrier ribs, characterized by being manufactured by: providing, before the first panel member and the second panel member are sealed together, the sealing material in a peripheral area of the first panel member or the second panel member so as to form a height that is greater than a height of the plurality of barrier ribs; and sealing, after the sealing material is provided, the first panel member and the second panel member by softening the sealing material while pressing the first panel member and the second panel member against each other in an area which is more central than the peripheral area.
With this construction, the sealing is performed with there being no gaps between the barrier ribs and the first panel member. Accordingly, the noise level of noise in the frequency range of 20 Hzxe2x80x9420 kHz, which occurs in the image display area when the first panel member and the second panel member vibrate during actual drive, can be limited to 30 dB or below.